05/31/2000 Env Bd Packet - Laserfiche WebLink

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ef.:2) Minnesota Pollution Control Agency ground water. Nitrate concentrations were greatest in oxygen -rich, high redox waters, while iron, manganese, arsenic, and boron all increased as redox potential decreased. Well diameter significantly affected water quality. The effect of well diameter was related to changes in redox conditions near large- diameter compared to small- diameter wells. Large - diameter wells had oxygen - rich, high redox water, which leads to elevated concentrations of nitrate and lower concentrations of iron and manganese compared to smaller- diameter wells. Large - diameter wells do not represent a major threat to an aquifer's water quality, despite these findings. Risk to ground water users was low for most aquifers and chemicals. The percentage of samples exceeding health -based drinking criteria was 8.7, 4.1, 3.3, and 2.3 for boron, manganese (using a standard of 1000 ug/L), nitrate, and beryllium, respectively. The percentage of samples exceeding their Maximum Contaminant Level (MCL) or Secondary Maximum Contaminant Level (SMCL) was 67.9, 6.5, and 3.7 for iron, aluminum, and sulfate, respectively. VOCs were detected in 11 percent of the wells, but there were only four exceedances of health -based drinking water criteria. The most common VOCs were chloroform (47 detections), toluene (26), xylene and benzene (13 each), di -, tri-, and tetrachoroethene (3, 5, and 4, respectively), and various chlorofluorocarbons (10). Atrazine was detected in two wells at concentrations below the drinking water standard. Analysis of individual parameters included an assessment of natural and anthropogenic sources for each chemical, the fate of chemicals in soil and ground water, factors affecting the observed distribution of chemicals in groundwater, and geochemical controls on distribution of chemicals in ground water. Who can use information from this study? The report is technical, but water planners can use the baseline information to better understand factors that may influence ground water quality. The `Summary Statistics' and the `Factors Affecting Ground Water Quality' sectior� of the report should help local water planners put what they already know about the local system into a larger context and determine if their area falls within expected ranges for parameters of concern. This document also contains information that should improve planners' understanding of the vulnerability and condition of their aquifer. This includes discussions of what parameters are of concern, which of those are naturally occurring, and which can be affected by human activity. This information can also be used to improve individual monitoring plans to get meaningful local information. Technical staff can use the baseline data to assess background conditions for aquifers and obtain information that may help make site decisions. The baseline document includes geochemical information that may help hydrogeologists to understand the conditions in certain aquifers. Another application is using the information to make risk -based decisions. Example scenarios of how this might be helpful are included in the full report in the summary and examples sections. Managers can use the baseline data to better understand ground water quality issues. It also will help managers toll understand potential risks to receptors and know what areas would benefit from ground water protection programs. The statistical summaries define background values for each aquifer, providing a context for Page 2 Baseline Water Quality of Minnesota's Principal Aquifers